This study includes ten annual surveys of levels of drug and alcohol use among junior and senior high school students in San Mateo County, California. Surveys using the same basic format have been conducted annually, 1968 through 1976, with a tenth projected for 1977. Every effort is made to enforce comparability between surveys. Levels of use of alcohol, amphetamines, LSD, marijuana, tobacco, barbiturates, heroin are queried. In cooperation with the Office of the County Superintendent of Schools, these surveys are administered across the County to all students in participating private, parochial and public schools. Each annual survey includes approximately 30,000 responses. This permits the observation of significant differences in patterns of use between sexes and grades. Significant differences in level of use by class/sex cohorts are also demonstrated over time. Such controlled observations can make a contribution toward setting up a general epidemic model for the growth of drug use in a particular population. This could have implications in long-range strategies for control. Multiple patterns of use are investigated. Results of the 1977 survey will permit an analysis of the impact of California legislation on marijuana trends, by sex and grade level.